Resonance energy transfer orientation factor

The optimal enhancement effect is observed when the localized surface plasmon resonance is tuned to the emission wavelength of a locally situated fluorophore [86]. This is consistent with the model suggesting a greatly increased efficiency for energy transfer from fluorophores to surface plasmons [78]. Since resonance energy transfer is involved, the important factors affecting the intensity of fluorescence emission must also be the orientation of the dye dipole moments relative to the... 

Wu P. and Brand L. (1992) Orientation Factor in Steady-State and Time-Resolved Resonance Energy Transfer Measurements, Biochemistry 31, 7939-7947. 

Dosremedios CG, Moens PDJ. Fluorescence resonance energy-transfer spectroscopy is arehable ruler for measuring structural changes in proteins. Dispelling the problem of the unknown orientation factor. Journal of Structural Biology 1995, 115, 175-185. 

Wu P, Brand L. Orientation factor in steady-state and time-resolved resonance energy transfer measurements. Biochemistry 1992 31 7939-7947. 

Fluorescence Resonance Energy Transfer (FRET), Fig. 1 (continued) the orientation factor from the relative alignment of the donor and acceptor transition dipoles, (d) ERET efficiency as a function of the relative distance between the donor and acceptor... 

According to Forster s theory [13], the efficiency of the resonance energy transfer ( ret) is inversely proportional to the sixth-power of the distance (r) between donor and acceptor (2). In (2), Rq is the so-called Forster distance at which the transfer efficiency is 50%. Forster RET is therefore a very sensitive process and can transduce small conformational changes into large intensity modulations. Rq is characteristic for a particular donor-acceptor pair and depends on the overlap integral J between >ret emission and Aret absorption, the PLQY of >ret in its unperturbed state < d and the mutual orientation of the two partners expressed as geometry factor which equals 2/3 for random orientation of the partners (3). For a more detailed discussion of the mechanistics of RET, the reader is referred to the literature [12]. 

Fig. 7.4 The orientation factor in the dipole-dipole interaction energy can vary from —2 to - -2. The rate of resonance energy transfer is proportional to...

Equations (7.13) and (7.17) indicate that, for widely separated molecules with a given intermolecular distance and orientation, the rate of resonance energy transfer is proportional to the product of the dipole strengths (Z7, a(i) and Dha(2))- The rate also depends on the thermally-weighted Franck-Condon factors for the pairs of downward and upward vibronic transitions that satisfy the resonance condition. These facts suggest that we can relate the rate to the absorption spectrum of the acceptor and the emission spectrum of the donor (Fig. 7.6). 

Equation (18) may be derived in a manner similar to that described above for vibration-vibration energy transfer, with the difference that the product of the squared matrix elements of the two vibrations concerned, appears in the expression for transition probability. Since both molecules require suitable orientation for vibrational exchange, for two diatomic molecules the steric factor is usually taken to be ( )2. If AE - 0 (exact resonance), eqn. (18) is no longer valid and the following equation may be employed... 

---